Four widely used in vitro assays for genetic toxicity were evaluated for their ability to predict the carcinogenicity of selected chemicals in rodents. These assays were mutagenesis in Salmonella and mouse lymphoma cells and chromosome aberrations and sister chromatid exchanges in Chinese hamster ovary cells. Seventy-three chemicals recently tested in 2-year carcinogenicity studies conducted by the National Cancer Institute and the National Toxicology Program were used in this evaluation. Test results from the four in vitro assays did not show significant differences in individual concordance with the rodent carcinogenicity results; the concordance of each assay was approximately 60 percent. Within the limits of this study there was no evidence of complementarity among the four assays, and no battery of tests constructed from these assays improved substantially on the overall performance of the Salmonella assay. The in vitro assays which represented a range of three cell types and four end points did show substantial agreement among themselves, indicating that chemicals positive in one in vitro assay tended to be positive in the other in vitro assays.

https://science.sciencemag.org/content/sci/236/4804/933.full.pdf

Prediction of chemical carcinogenicity in rodents from in vitro genetic toxicity assays.

D. B. Owen: Handbook of Statistical Tables. London: Pergamon Press; Reading, Massachusetts: Addison‐Wesley, 1962. Pp. xii+580. 70s.

Handbook of Statistical Tables.

Results from the testing of 108 coded chemicals in Chinese hamster ovary (CHO) cells for the induction of chromosome aberrations and sister chromatid exchanges (SCEs) are presented. All chemicals were tested with and without exogenous metabolic activation, using protocols designed to allow testing up to toxic doses. Cell harvest times could also be extended if chemical-induced cell cycle delay was seen. Chromosome aberrations were induced by 43 of the chemicals, and 66 induced SCEs; 37 of the chemicals were positive for both endpoints.

Chromosome aberrations and sister chromatid exchanges in chinese hamster ovary cells: Evaluations of 108 chemicals

Mammalian in vivo cytogenetic assays. Analysis of chromosome aberrations in bone marrow cells.

The protocol recommended for the micronucleus assay in mammalian bone marrow has been revised and simplified. The number of sample times has been reduced to one or two, depending upon the dosing protocol. The minimum number of cells to be scored per treatment group has been increased to 20,000 to increase the ability of the assay to detect a doubling of the control micronucleus frequency. Use of both male and female animals is recommended. Scoring of micronuclei in polychromatic erythrocytes of peripheral blood is included as a variation of the bone marrow assay. Published data on chemicals tested by the micronucleus assay have been reviewed and are summarized.

The in vivo micronucleus assay in mammalian bone marrow and peripheral blood. A report of the U.S. Environmental Protection Agency Gene-Tox Program

It is a widely held view that objective statistical criteria are needed for the evaluation of genetic toxicity assays. This paper presents statistical methods for the analysis of data from in vitro sister chromatid exchange (SCE) and chromosome aberration tests that use Chinese hamster ovary cells. For SCEs, an extensive study of solvent control results demonstrated that there is a substantial interday component of variability in the data, and that a Poisson sampling model is applicable to data generated via the protocol of Galloway et al [1985]. Consequently, a trend test for evidence of a dose response is proposed for such SCE data. As an illustration of this statistical method, analysis of data previously considered to be negative [Gulati et al, 1985] indicates that di(2-ethyl-hexyl) phthalate induces a weak, but reproducible, SCE dose response in CHO cells. Monte Carlo methods are used to show that the trend test is more sensitive than four other statistical procedures considered for the analysis of Poisson-distributed SCEs. A similar trend test for dose response in proportions is proposed for chromosome aberration data, where the percent of cells with chromosome aberrations is the response of interest. Sensitivity (or power) studies indicate that three doses and a control with 50 cells/dose point is a reasonable design for an in vitro SCE study that uses the Galloway et al protocol. For in vitro chromosome aberrations, however, three doses and a control with 100 cells/dose point appears to produce too insensitive an assay; an increase to 200 cells/dose point in the Galloway et al protocol seems worthy of serious consideration.

J. Y. Rimpo

Papers

Statistical analyses for in vitro cytogenetic assays using Chinese hamster ovary cells